About the J2EE Containers

Types of J2EE Containers

J2EE containers provide runtime support for J2EE application components. J2EE
application components use the protocols and methods of the container to access other
application components and services provided by the server. The Application Server provides
an application client container, an applet container, a Web container, and an EJB
container. For a diagram that shows the containers, see the section Application Server Architecture.

The Web Container

The Web Container is a J2EE container that hosts web applications. The web container
extends the web server functionality by providing developers the environment to run servlets and JavaServer Pages (JSP files).

The EJB Container

There are three types of enterprise beans: session beans, entity beans,
and message-driven beans. Session beans represent transient objects and processes
and typically are used by a single client. Entity beans represent persistent data,
typically maintained in a database. Message-driven beans are used to pass messages
asynchronously to application modules and services.

The container is responsible for creating the enterprise bean, binding the
enterprise bean to the naming
service so other application components can access the enterprise bean, ensuring only authorized
clients have access to the enterprise bean’s methods, saving the bean’s
state to persistent storage, caching the state of the bean, and activating
or passivating the bean when necessary.